Honeywell AUTOMATIC CONTROL SI Edition, Engineering Manual

Page: 390 / 512

ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
380
DISTRICT HEATING APPLICATIONS
HEAT SOURCES
Sources of heat to supply the network include waste
incineration plants, boiler houses, heat pumps, and waste heat
from electric power generating plants, steel foundries, or similar
industrial processes.
A combined heat and power plant (CHP) which generates
electricity using a steam turbine or an engine is probably the
most common heat source. It heats the heating medium in the
distribution network using the exhaust gases leaving the turbine.
Because these systems are parts of an industrial processes,
control components and systems are typically industrial
standard. Control components and systems are chosen to meet
the requirements of the heat source and the specifications.
THE DISTRIBUTION NETWORK
Pipelines transfer heat from where it is generated to the
consumer. Depending on the heat source, the distribution
network generally consists of pairs of supply and return pipes.
Hot water flows continuously through the supply pipes to the
substations, heats the secondary fluid in heat exchangers, and
returns to the heat source through the return flow pipes.
The distribution network facilities also include booster pumps
and pressure reducing stations, mixing (temperature reducing)
stations, key-points with valves to turn on or shut off branch
lines and a large number of measuring points distributed over
the entire network.
INTRODUCTION
District Heating (DH), refers to a method of supplying heat
to buildings, factories, and other facilities from a central source.
The basic structure of District Heating Systems is shown in
Figure 126. A DH System consists of one or more heat
generating facilities, a widely spread heat distribution network,
and substations between the distribution network and the
consumer. Heat is generated by the heat source(s) and
transferred to an appropriate heating medium such as hot water
or steam. The heating medium is transported via pipelines to a
substation. In the substation heat is transferred to the individual
heating systems of the end-users.
Space heating, space cooling, and domestic hot water supply
represents the largest part of energy consumption (75%) in
buildings and industries. This demand is met mainly by fossil
fuels and electrical energy. At the same time a vast amount of
waste heat is discharged into the atmosphere by power and waste
incineration plants and other industrial processes. The efficiency
of current power plants does not exceed 50%.
District heating brings the waste heat directly to the customers
as a salable product. This makes individual furnaces redundant.
Additional advantages result from higher efficiency of central
heat generation, lower emissions, and the capability of fuel
diversification by using the fuel with the lowest price and the
best availability. A central energy supply, based on combined
heat and power generation has an overall efficiency of up to
80%. Additionally it shows a considerable emissions reduction
from reduced fuel consumption.
M11434
STEAM
FUEL 100%
LOSS 10%
OTHER LOSSES 5%
POWER 35 – 40%
GENERATOR
COOLING WATER
LOSS 10 – 35%
FEED WATER
HEAT 40 – 10%
PSF
SSF
SRF
PRF
SUBSTATION
(HEAT EXCHANGER)
BUILDING
(CUSTOMER)
BOILER
TURBINE
HEAT GENERATION
DISTRIBUTION
Fig. 126. District Heating Network.